Automatic control mechanism



I y 1935-. G. P. E. HOWARD 2,901,348

AUTOMATIC CONTROL MECHANISM Filed Jan. 13, 1933 Patented May 14, 1935 v UNITED STATES PATENT or-Pics AUTOMATIC WNIBOL ME one; run, Eliot Howard, Lnton. England, assignor to Messrs. George Kent Limited, London, England Application January 13, 1933, Serial No. 351,638

8 Claims. r (01. 236-43) provide an arrangement which-shall be simple to construct, and shall consist of a minimum of parts with consequent reduction in frictional losses and thus requiring small operating force.

The invention is illustrated in the accompanying drawing in which Figure 1 is a tic elevation partly in section, Figure 2 a detail view, A

and Figure 3 is a fragmentary vertical sectional view on the line 3-3 of Figure l with some parts shown in elevation.- The particular apparatus shown is arranged to effect control of a gas ted furnace through an opposed fluid pressure nozzle as is claimed in the specification of United States Letters Patent of J. L. Hodgson et al., No. 1,953,406, issued May 5, 1934, but it will be understood that the invention is capable of application to control generally. l

I is a furnace which is heated by a burner 2 fed with gas through a pipe 3' having a control valve 4 therein. 5 is a thermostatic device which is responsive to the value of the temperature of the furnace and is placed in connection through a capillary tube 6 with a device I which, in response to temperature change, produces a movement of an arm 8. This arm is connected by a link 9 to an arm l having a recording pen thereon, the pen moving over a chart l2 supp rted by a carrier |2a driven at a predetermined constant speed by a clockwork motor ,l3 through gearing II. This arm I0 is mounted to rock about a pivot IS on which is also mounted a second arm l6 which is connected by a link IT to a setting device comprising an arm l8 and rotatable member l9 having a groove 20 to receive an operating key which is conveniently the key for winding the motor I3. The arrangement may be such that it 7 is necessary to unlock the casing (indicated at l9) to gain access to the rotatable member. The arms l0, l6 are provided with pairs of pins 2|, 22, and 23, 24: which are arranged to receive an arm 25 which is formed at one end with an 23 whose other end is connected to a chopper blade 29 which is pivotally mounted at 3|! and is arranged to be moved more or less into the path or a fluid stream passing from a nozzle 3| to a nozzle 32. which latter is placed in communication through apipe 33 with a diaphragm 34 having a rod 33 coupled to the valve 4. The arrangement is such that when the'arm I3 is coincident with the arm It the pin 2! lies over the pivot I5 and thus simultaneous movement of the two arms In,

3 would not cause any relative movement of the arm 25. If however the arm "I moves with respect to the arm It (as would occur when'the temperature varied from the desired value as indicated by the am Hi) the arm 25 is caused by reason of the pin and slot connection 2|, 26 to rock about its connection with the arm l6 and this movement is transmitted to the link 28 and thence to the chopper blade 28 which in turn varies the effective fluid pressure transmitted to the diaphragm 34 which finally produces movement of the fuel control valve 4. This control will continue until the value of temperature is restored to the desired value.

It will be observed that a minimum of parts are provided and also that the arm I0 is enabled to move with respect to the arm IS without restraint. It will also be. observed that when the arm 25 engages the pins 2|, 24, the arm 25 has a substantial movement towards a position in line with the link 28 as the arm I8 is moved towards the upper limit of the temperature control (1. e. as the arm is rocked in a clockwise direction) and thus for a given angular separation between the two arms l3, IS the arm |8transmits a smaller movement to the link 23 when the arm I3 is set nearer the upper limit than when the arm I6 is a set nearer the lower limit and thus the sensitivity or control is a maximum. at the lower limit and a minimum at the upper limit. The pins 22, 23 however provide an alternative in which the sensitivity is more or less constant over the whole control range, this being eifected for the reason that in a mid position of the arm IS the arm is at or substantially at right angles to the link when the arms |3, |3 are coincident. i

In order to provide for a varying extent of movement of the chopper blade 29 for a given movement oi the link 28 a plurality of apertures 36 is provided which are spaced at ,difierent' distances from the pivot of the blade and in order that the blade may be moved either to obstruct or to clear the fluid stream with change in temperature the arrangement may be such as to enreached a position corresponding to a predetermined value.

It will be seen that an arrangement according to the invention possesses the following features which are esential in an eilicient control appsratus:

(c) There is provided a pointer or indicator which shows atall times the value at which the controller is set to maintain the condition, e. g. the value 0! temperatine.

@(blThe setting pointer is unaffected by the movements of the measuring mechanism so that the setting pointer indicates the set value whether the true or actual value coincides with the set value or not.

(c) The setting pointer moves over the same scale as the indicating pointer or recording pen so that when the true value is that at which the controller is set the indication afforded by the setting pointer and the indicating pointer or pen coinsides.

(d) The setting pointer has intrinsically the same scale calibration as the indicating pointer or pen.

(e) The set value 01 the quantity can be varied according to any required time cycle and this is eflected by the clock or other means employed to rotate the record chart.

(I) The control mechanism is enabled to be made more sensitive at small values of the varable than at large values and thus uniform ac curacy of control may be obtained. It may here be pointed out that a given variation of temperature or other variation from the desired value when this is set at the lower limit of the apparatus will require a larger operation of the controls to cause the conditions to return to the desired value than will the same value oi. deviation of the conditionat the upper limit of the apparatus, the deviation at the upper limit being a smaller fraction of the value of condition than the same deviation at the lower limit. In addition, this-variable sensitivity enables the invention to be applied to the scale or record, that is to say, the lowest value shown on the scale or chart has some other be controlled, a' third arm pivotally connected to the setting arm and placed in connection with the. second arm through a pin and slot connection 1 a control means, a link connecting the control means to the third arm, the point of connection of the link to the third arm being co-axial with the pivotal axis of the setting-and second arms when these latter min a predetermined relative position whereby similar movement 0! the setting and second arms produces no relative movement of the third arm while deparature of these arms from the predetermined relative position effects movement of the third arm and hence of the control device in dependence on the extent of departure.

2. In automatic control mechanism, the combination of a setting arm for setting the mechanism to the value at which it is desired to maintain the condition to be'controlled, a second arm which is mounted to rock about an axis concentric with that of the setting arm and is displaced in dependence on the valueof the condition to be controlled, a third arm pivotally connected to the setting arm and placed in connection with the second arm through a pin and slot connection, a control means, a link connecting the control means to the third arm, the point of connection ot the link to the third arm being coaxial with the pivotal axis oi the setting and second arms when these latter are in a predetermined relative position whereby similar movement of the setting and second arms produces no relative movement of the third arm while departure of these arms from the predetermined relative position eilects movement of the third arm and hence of the control device in dependence on 'the extent oi departure, the relative position of .the third arm and the link being so determined by the points of connection of the arm to the setting and second arms that as the value desired moves towards the upper limit oi the mechanism the third arm has a substantial movement towards a position in line with the link so that for a given movement of the third arm in response to separation between the setting and second arms the movement transmitted to the link decreases to reduce the sensitivity of the mechanism.

3. In automatic control mechanism, the combination of a setting arm, a second arm which is displaced in dependence on the value of the condition to be controlled, means operatively connected to and inter-relating the two arms in such manner that the second arm can move without restraint by the setting arm, the inter-relating means being adapted to be actuated by the second arm to an extent dependent on the relative positions of the two arms, andcontrol means .which are actuated by the inter-relating means to sheet automatic control 0! the condition to be controlled, the inter-relating means being such as to transmit a smaller movement to the control means as the desired value of control approaches the-upper limit of the mechanism.

- relative. position whereby,

' to the'value at which it is desired to 7 tain the condition to be controlled, means ior cauiiing the setting arm, to assume diflerent positi' during a control period, a second arm w 6b is mounted torock about an axis concentrio. with that oithe setting arm and is displaced in dependence on the value of the condition to be controlled, a third'arm pivotally connected to the setting arm and. placed in connection with the second arm through a pin and slot connection, a control means, a link connecting the control means to the third arm, the point of connectionotthelinktothethirdarmbeingco-axiai with the pivotal axis of the setting and second arms when these latter are in apredetermined similar movement or. the setting and arms produces'no relative movement or the third arm while departure of these arms from the predetermined relativeposition eflfects movement of the third arm and hence of the control device in dependence on the extentoideparture. Y Y In automatic control mechanism, the com-- bination of a setting arm for setting the mechanism to the value at which it is desired to mainta'in the condition to be controlled, means for causing the setting armto assume. diflerent positions during a control period, ;a second arm which is mounted to took about an axis concentric with that of the setting arm and is displaced in dependence on the value of the condition to be controlled, a chart carrier, the setting and second-arms being adapted to indicate their respective values by reference to a chart on the carrier, a third arm .pivotally connected to the settin arm and placed in connection with the second arm through a pin and slot connection, a control means. a link connecting the control means to the third arm, the point of connection at the link to the third arm being c'o-axi'al with the pivotal aids oi the setting and second arms when these latter are in a predetermined relative position whereby similar movement of the setting and second arms produces no'relative movement of the third arm while departure of these arms from the predetermined relative position eilects mover trolled, the

device in dependence on the extent of departure.

6 In automatic control mechanism, the combinati'on-oi a setting arm, a second arm which is dispiacedin dependence on the value of the-condition to be controlled, means inter-relating the two arms in such manner that the second arm can move without .restraint by the setting arm and such as to be actuated by the second arm to an extent dependent on the relative positions oi the two arms, and control means which are actuated by the inter-relating means to eflect automatic control of the condition to be coninter-relating means being capable of alternative connection with the setting and second arms and being in one position arranged to transmit a smaller movement to the control as the desired value of control moves towards the upp f limit of the mechanism and in the second position to transmit. a substantially constant movement to the control means over the whole range of control.

'7. Mechanism as claimed in claim 2 and in which an alternative position of the third arm relatively to the setting and second arms is provided, in which alternative position a substantially constant movement, is imparted tothe link in response toseparation between the setting and second arms over the whole control range of the mechanism.

8. In automatic control apparatus for controlling a variable condition, the combination of means for setting the apparatus within upper and lower limits to maintain a predetermined value of the condition, means responsive to changes in the condition, control means, and means so inter-relating the setting, the responsive, and the control means that, while the control means is caused to operate throughout the range 0! the apparatus to an extent dependent on the departure of the condition from the desired predetermined value, a givenextent of operation oi the control means is produced by a deviation which increases from a minimum at the lower limit or the apparatus to a maximum at the upper limit of the apparatus.

GILES PHILIP ELIOT HOWARD.

' ment oi the third arm and hence of the control 

